In some wireless communication systems, the decoding of an information-bearing codeword (CW2) requires that another information-bearing codeword (CW1) be decoded correctly. CW2 may thus be denoted by the term “compound codeword” as decoding of CW1 is essential for the correct decoding of CW2. For example, CW1 could contain information regarding transmission parameters used in transmitting CW2 which are essential for the decoding of CW2. The transmission parameters may include the number of OFDM symbols on which CW2 is transmitted, or the time-frequency sub-carrier mapping used for carrying CW2, (e.g., start and range of resource elements in the time-frequency grid on to which the codeword is mapped), or coding scheme (e.g., block code, convolutional code, turbo-code, etc.), or a code-rate, or block size, or encoded information bit length, or modulation type, or a redundancy version number of the codeword in a hybrid ARQ transmission using incremental redundancy, or transmit antenna type (e.g., SIMO, Tx diversity, spatial multiplexing, etc.), or the precoding used, or the transmission rank, etc.
CW1 and CW2 may correspond to a block code (linear or otherwise) or a convolution code or a turbo-code or an uncoded transmission. Generally, a receiver decodes CW1 first and then tries to decode to CW2. Suppose a receiver wants to predict the practical decoder performance of CW2, then it has to jointly consider this with the fact that decoding of CW1 can be erroneous. In E-UTRA standard, one application of the above method is for obtaining an estimate of overall error probability of PDCCH. In this example, CW1 corresponds to a physical control formatting indicator channel (PCFICH) which contains information about the PDCCH codeword transmission parameters like the number of OFDM symbol containing control information in the subframe under different deployment configurations as specified in Table 6.7-1 of 36.211 and Table 5.3.4-1 of 36.212 reproduced below:
TABLE 6.7-1Number of OFDM symbols used for PDCCHNumber of OFDMNumber of OFDMsymbols for PDCCHsymbols for PDCCHSubframewhen NRBDL > 10when NRBDL ≦ 10Subframe 1 and 6 for frame1, 22structure type 2MBSFN subframes on a1, 22carrier supporting bothPMCH and PDSCH for 1or 2 cell specificcantenna portsMBSFN subframes on a22carrier supporting bothPMCH and PDSCH for 4cell specific antennaportsMBSFN subframes on a00carrier not supportingPDSCHAll other cases1, 2, 32, 3, 4
TABLE 5.3.4-1CFI CodewordsCFI codewordCFI<b0, b1, . . . , b31>1<0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1,1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1>2<1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0,1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0>3<1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1>4<0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,(Reserved)0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>
CW2 corresponds to a physical downlink control CH (PDCCH) codeword. The correct decoding of PCFICH is necessary for correctly decoding the PDCCH codeword. The channel state information corresponding to the PCFICH transmission can be used to estimate the block error rate using a mapping function that uses the subcarrier level SINR information. Another mapping function that uses the subcarrier level SINR information can be used to obtain the conditional probability of error in decoding the PDCCH under the assumption that PCFICH has been decoded correctly.
In another example, in an E-UTRA link, suppose that a physical downlink shared channel (PDSCH) codeword is scheduled by DCI information embedded in a PDCCH codeword. Then correct decoding of the PDSCH codeword is dependent on correct decoding of both PDCCH that contains scheduling information and the PCFICH codeword.
Methods for estimating BLER corresponding to a coded packet transmission from the subcarrier SINR information in an OFDM system are known generally. Two of the well-known methods, effective exponential-sum-of-SINR mapping (EESM) and mean mutual information per bit (MMIB) mapping, use the principle that the average BLER function corresponding to a packet transmission with a fixed set of parameters such as encoding type, codeword length, information size (or alternately code rate), modulation type, etc. can expressed in terms of basis functions of the appropriate type. A third method is to map instead the first few moments of the sample sub-carrier SINR distribution to BLER. The EESM, MMIB and the third approach are listed below as applied to OFDM systems.
Suppose that two codewords CW1 and CW2 are transmitted. Correct decoding of CW1 is necessary for the correct decoding of CW2 as transmission parameters associated with CW2 are embedded in CW1. Now, suppose that a receiver wants to estimate the block error rate of decoding CW2. The probability of correct decoding CW2 conditioned on the correct decoding of CW1 might be different from the probability of correct decoding of CW2. This can happen due to one of more of the following side conditions: 1. Difference in code-rates, block-sizes of the different codewords; 2. Coding schemes used for the encoding of the information embedded in the two codewords; and 3. Operating SINR-point, interference statistics, etc. In the prior art, the problem of predicting the block error rate of a codeword when such dependencies exist has not been addressed.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.